<template>
<scroll class="listview"
        :data="data"
        ref="listview"
        :listenScroll="listenScroll"
        :probeType="probeType"
        @scroll=scroll>
  <ul>
    <li v-for="(group,index) in data" class="list-group" :key="index" ref="listGroup">
      <h2 class="list-group-title">{{group.title}}</h2>
      <ul>
        <li @click="selectItem(item)" v-for="(item,index) in group.items" :key="index" class="list-group-item">
          <img v-lazy="item.avatar" alt="" class="avatar">
          <span class="name">{{item.name}}</span>
        </li>
      </ul>
    </li>
  </ul>
 <div class="list-shortcut" @touchstart="onShortcutTouchStart" @touchmove.stop.prevent="onShortcutTouchMove">
     <ul>
         <li v-for="(item, index) in shortcutList"
         :key="index"
         class="item"
         :class="{'current': currentIndex === index}"
         :data-index="index">
           {{item}}
          </li>
     </ul>
</div>
<div class="list-fixed" v-show="fixedTitle" ref="fixedTitle">
    <div class="fixed-title">{{fixedTitle}}</div>
</div>
<div class="loading-container" v-show="!data.length">
     <loading></loading>
</div>
</scroll>
</template>

<script type="text/ecmascript-6">
import Scroll from 'base/scroll/scroll'
import {getData} from 'common/js/dom'
import Loading from 'base/loading/loading'
const ANCHOR_HEIGHT = 18
const TITLE_HEIGHT = 30
export default{
  created() {
    this.touch = {}
    this.listenScroll = true
    this.listHeight = []
    this.probeType = 3
  },
  data() {
    return {
      scrollY: -1,
      currentIndex: 0,
      diff: -1
    }
  },
  props: {
    data: {
      type: Array,
      default: () => {
        return []
      }
    }
  },
  computed: {
    shortcutList() {
      return this.data.map((group) => {
        return group.title.substr(0, 1)
      })
    },
    fixedTitle() {
      if (this.scrollY > 0) { // 判断边界，‘热门’往上拉时，不显示
        return ''
      }
      // 初始时，data默认为空，此时this.data[this.currentIndex]为undefinded
      return this.data[this.currentIndex] ? this.data[this.currentIndex].title : ''
    }
  },
  methods: {
    selectItem(item) {
      this.$emit('select', item)
    },
    onShortcutTouchStart(e) {
      let anchorIndex = getData(e.target, 'index')
      let firstTouch = e.touches[0]
      this.touch.y1 = firstTouch.pageY
      this.touch.anchorIndex = anchorIndex
      this._scrollTo(anchorIndex)
    },
    onShortcutTouchMove(e) {
      let firstTouch = e.touches[0]
      this.touch.y2 = firstTouch.pageY
      let delta = (this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT | 0
      let anchorIndex = parseInt(this.touch.anchorIndex) + delta
      this._scrollTo(anchorIndex)
    },
    refresh() {
      this.$refs.listview.refresh()
    },
    scroll(pos) {
      this.scrollY = pos.y // 实时获取BScroll滚动的Y轴距离
    },
    _calculateHeight() {
      this.listHight = [] // 每次重新计算每个group高度时，恢复初始值
      const list = this.$refs.listGroup
      let height = 0 // 初始位置的height为0
      this.listHeight.push(height)
      for (let i = 0; i < list.length; i++) {
        let item = list[i] // 得到每一个group的元素
        height += item.clientHeight // DOM元素可以用clientHeight获取元素高度
        this.listHeight.push(height) // 得到每一个元素对应的height
      }
    },
    _scrollTo(index) {
      // console.log(index)
      if (!index && index !== 0) {
        return
      }
      if (index < 0) {
        index = 0
      } else if (index > this.listHeight.length - 2) {
        index = this.listHeight.length - 2
      }
      this.scrollY = -this.listHeight[index]
      this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 0)
    }
  },
  watch: {
    data() {
      setTimeout(() => {
        this._calculateHeight()
      }, 20)
    },
    scrollY(newY) {
      const listHeight = this.listHeight
      // 当滚动到顶部，newY>0
      if (newY > 0) {
        this.currentIndex = 0
        return
      }
      // 在中间部分滚动，遍历到最后一个元素，保证一定有下限，listHeight中的height比元素多一个
      for (let i = 0; i < listHeight.length - 1; i++) {
        let height1 = listHeight[i]
        let height2 = listHeight[i + 1]
        if (-newY >= height1 && -newY < height2) {
          this.currentIndex = i
          this.diff = height2 + newY
          // console.log(this.currentIndex)
          return
        }
      }
      // 当滚动到底部，且-newY大于最后一个元素的上限
      // currentIndex 比listHeight中的height多一个, 比元素多2个
      this.currentIndex = listHeight.length - 2
    },
    diff(newVal) {
      let fixedTop = (newVal > 0 && newVal < TITLE_HEIGHT) ? newVal - TITLE_HEIGHT : 0
      if (this.fixedTop === fixedTop) {
        return
      }
      this.fixedTop = fixedTop
      this.$refs.fixedTitle.style.transform = `translate3d(0, ${fixedTop}px, 0)`
    }
  },
  components: {
    Scroll,
    Loading
  }
}
</script>
<style scoped lang="stylus" rel="stylesheet/stylus">
@import '~common/stylus/variable';

.listview {
  position: relative;
  width: 100%;
  height: 100%;
  overflow: hidden;
  background: $color-background;

  .list-group {
    padding-bottom: 30px;

    .list-group-title {
      height: 30px;
      line-height: 30px;
      padding-left: 20px;
      font-size: $font-size-small;
      color: $color-text-l;
      background: $color-highlight-background;
    }

    .list-group-item {
      display: flex;
      align-items: center;
      padding: 20px 0 0 30px;

      .avatar {
        width: 50px;
        height: 50px;
        border-radius: 50%;
      }

      .name {
        margin-left: 20px;
        color: $color-text-l;
        font-size: $font-size-medium;
      }
    }
  }

  .list-shortcut {
    position: absolute;
    z-index: 30;
    right: 0;
    top: 50%;
    transform: translateY(-50%);
    width: 20px;
    padding: 20px 0;
    border-radius: 10px;
    text-align: center;
    background: $color-background-d;
    font-family: Helvetica;

    .item {
      padding: 3px;
      line-height: 1;
      color: $color-text-l;
      font-size: $font-size-small;

      &.current {
        color: $color-theme;
      }
    }
  }

  .list-fixed {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;

    .fixed-title {
      height: 30px;
      line-height: 30px;
      padding-left: 20px;
      font-size: $font-size-small;
      color: $color-text-l;
      background: $color-highlight-background;
    }
  }

  .loading-container {
    position: absolute;
    width: 100%;
    top: 50%;
    transform: translateY(-50%);
  }
}
</style>
